Octreotide treatment in acromegaly: a comparison between pen-treated and pump-treated patients in a cross-over study

Octreotide LAR: safety and tolerability issues

BACKGROUND

Somatostatin analogues are the cornerstone in therapy of acromegaly and functioning neuroendocrine tumors. Long-acting retard formulations have improved patient survival and contributed considerably to quality of life. The first such compound was octreotide LAR ('long-acting release'), characterized by high affinity to somatostatin receptor subtypes 2 and 5, which has to be injected intramuscularly every 4 weeks.

OBJECTIVE

The aim was to screen all octreotide LAR-related literature and assess the compound's profile for safety and tolerability.

METHODS

An extensive literature search has been performed using the MEDLINE database to retrieve data from clinical studies evaluating the efficacy and tolerability of octreotide LAR.

RESULTS/CONCLUSION

Octreotide LAR is well tolerated; however, diarrhea and gallstone formation were identified as the main adverse events. Impairment of glucose homeostasis was a regular phenomenon, but its occurrence was unpredictable. General side effects such as headache, abdominal discomfort or fatigue were also reported. According to incidental case reports, administration during pregnancy appears to be safe for both mother and child; however, definitive evidence is missing. In addition, octreotide LAR has been evaluated for further indications including treatment of solid tumor entities, due to its antiproliferative effect. Currently, several compounds (lanreotide, SOM230) with a broader receptor spectrum are under evaluation and may improve treatment efficacy and lower incidence of side effects.

Octreotide for acromegaly

Octreotide has dramatically changed the results of medical treatment of acromegaly. It is the reference drug for the pharmacological treatment of acromegaly, owing to its impressive efficacy in suppressing growth hormome secretion, and excellent compliance. Safe growth hormone and normal insulin-like growth factor I values are reached in 50-60% of unselected patients. Octreotide arrests the growth of the tumor and shrinks tumor in over half of all patients (namely, up to 88% of naive patients and to complete disappearance in anecdotic cases). The safety profile of octreotide is excellent, but in some patients, glucose metabolism worsens and cholelythiasis occurs. This review will address the primary treatment and the relative roles of pharmacological and surgical treatment, as well as the predictivity of octreotide results.

Current status and future opportunities for controlling acromegaly

Growth-hormone (GH) secreting adenomas, including acromegaly, account for approximately one-sixth of all pituitary adenomas and are associated with mortality rates at least twice that of the general population. The ultimate goal of therapy for acromegaly is normalization of morbidity and mortality rates achieved through removal or reduction of the tumor mass and normalization of insulin-like growth factor I (IGF-I) levels. Previously published efficacy results of current treatment modalities (surgery, conventional radiation, and medical therapy with dopamine agonists and somatostatin analogs) are often difficult to compare because of the different criteria used to define cure (some of which are now considered inadequate). For each of these modalities, pooled data from a series of acromegaly studies were reviewed for rates of IGF-I normalization, a currently accepted definition of cure. The results showed overall cure rates of approximately 10% for bromocriptine, 34% for cabergoline, 36% for conventional radiation, 50-90% for surgery for microadenomas and less than 50% for macroadenomas, and 54-66% for octreotide. These cure rates based on IGF-I normalization are generally less than those reported for cure based solely on GH levels. Novel new therapies for acromegaly include the somatostatin analog, lanreotide, Gamma Knife radiosurgery, and pegvisomant, the first in its class of new GH receptor antagonists. Although it does not appear that Gamma Knife radiosurgery results in significantly higher cure rates or fewer complications, it does provide a notable improvement in delivery compared with conventional radiation. Early studies have reported IGF-I normalization in 48% of lanreotide-treated patients and up to 97% of pegvisomant-treated.

GH/IGF-I normalization and tumor shrinkage during long-term treatment of acromegaly by lanreotide

New depot somatostatin analogs such as lanreotide-slow release (LAN) represent a significant improvement in the medical treatment of acromegaly. Seventy-three consecutive acromegalic patients, treated by LAN, were evaluated in a retrospective monocentric study. Sixteen were excluded from further evaluation due to combined treatment with dopamine agonist drugs, early LAN withdrawal for persistence of headache, or gastrointestinal side-effects. Fifty-seven patients (aged 20-82 years, 16 males) were thus evaluated. Thirty-two patients had been previously treated by neurosurgery (Tx) and/or radiotherapy (Rx). After washout, LAN (30 mg) was administered im at 10-14-day intervals. Time intervals between injections were then individually tailored to normalize IGF-I levels. LAN was administered for 12 (6-36) [median (range)] months. GH and IGF-I levels decreased from 13 (7-20) [median (interquartile)] microg/l to 3.2 (1.7-6.2) microg/l (p<0.0001) and from 780 (596-1000) microg/l to 264 (180-530) microg/l (p<0.000001), respectively. Seven patients were resistant to treatment. Among the 50 sensitive patients, GH levels fell below 2.5 microg/l in 52% (and below 1 microg/l in 18%), IGF-I levels normalized in 72% and both results were obtained in 46%. IGF-I values normalized in 87% of patients treated every 14 days, in 100% every 21-28 days, in 69% every 10 days and in 22% every 7 days. No different control of GH/IGF-I hypersecretion was evidenced between patients previously treated or not by Tx and/or Rx. Patients with the lowest basal hormonal levels and those over 55 years showed greater responsiveness (both p<0.05). The maintenance of LAN schedule up to 18 months determined a further suppression (p=0.04 for IGF-I). A reduction of tumor size was shown in 60% of evaluated patients (6/10). HbA1c slightly increased in 42% of patients and gallstones were observed in 16%. LAN is a very effective tool in the treatment of acromegaly: its chronic administration normalizes GH/IGF-I levels in most patients, shrinks the tumor in a high percentage of patients and seems to control hormonal hypersecretion as primary treatment as well as neurosurgery.

Continuous versus intermittent subcutaneous infusion of octreotide in the treatment of acromegaly

This review evaluates the efficacy, tolerability, and safety of continuous subcutaneous infusion (CSI) relative to intermittent subcutaneous injection (ISI) of the somatostatin analog, octreotide in the treatment of acromegaly. Data was extracted from five clinical series using CSI octreotide in acromegaly, six reports comparing CSI to ISI, and three studies comparing pulsatile subcutaneous infusion (PSI) to ISI. Effects of each drug regimen on the control of growth hormone (GH), insulin-like growth factor (IGF-1), clinical symptomatology, pituitary tumor size, and adverse effects were evaluated. Normalization of serum GH or IGF-1 levels, as well as improvement in clinical symptoms was reported in the majority of the patients studied. Cases in which pituitary adenomas decreased in size were also documented during the study period. When the effects of CSI were compared with ISI, a more pronounced control of GH and IGF-1 was observed. In addition, diurnal GH fluctuation during CSI was significantly reduced relative to ISI in two reports. Moreover, in two patients, CSI achieved similar clinical and biochemical effects at lower doses than when the drug was given by ISI. Finally, adverse effects with CSI may be less severe than with ISI. Continuous subcutaneous infusion of octreotide produced biochemical improvement in 67 of the 88 patients reviewed. When compared with ISI, CSI induced more pronounced biochemical control, often with less fluctuation in GH and IGF-1 levels. Because of a lack of data, definite conclusions regarding the differences between regimens on clinical symptomatology and tolerability could not be discerned. A large prospective, long-term randomized crossover study is recommended to make these determinations.

Treatment of invasive growth hormone pituitary adenomas with long-acting somatostatin analog SMS 201-995 before transsphenoidal surgery

The purpose of this study was to determine whether the long-acting somatostatin analog SMS 201-995 (octreotide) shrinks growth hormone (GH)-secreting adenomas and improves the results of subsequent transsphenoidal surgery. Ten previously untreated active acromegalic patients (nine women and one man) with invasive tumors were treated with SMS 201-995 (100 micrograms subcutaneously every 8 hours) for 6 weeks prior to transsphenoidal surgery. The clinical activity, mean GH secretion, insulin-like growth factor (IGF)-I concentration, and tumor volume were measured under basal conditions and on Days 14, 28, and 42 of treatment. The SMS 201-995 improved the symptoms of acromegaly in all patients. Mean levels of both GH and IGF-I (+/- standard deviation) were significantly decreased by Day 14 (from 92.9 +/- 30.5 to 44.9 +/- 20.3 micrograms/liter and from 10.6 +/- 7.4 to 5.9 +/- 2.6 U/ml, respectively), after which there were only slight further decreases. Six (60%) of the 10 patients experienced tumor shrinkage ranging from 9% to 78% (mean 30%). When it occurred, tumor shrinkage was significant by Day 14 (7.9 +/- 6.3 to 6.5 +/- 5.1 cu cm) and no further shrinkage was achieved by longer administration. Transsphenoidal surgery reduced postoperative GH levels to less than 2 micrograms/liter and IGF-I to less than 1.5 U/ml in six patients (60%). This percentage of cure is higher than expected from the literature and the authors' previous experience. However, an investigation of the influence of this drug on several parameters, such as reduction of tumor size or GH and IGF-I concentrations, has failed to prove any relationship. Only pretreatment size of the tumor was of predictive value with respect to the surgical outcome.

The pulsatile GH secretion in acromegaly: hypothalamic or pituitary origin?

OBJECTIVE

We studied the effects of different modes of octreotide therapy on the pulsatile pattern of GH release in an attempt to define better its regulation by growth hormone-releasing hormone (GHRH) and somatostatin and its effects on IGF-I plasma levels in acromegaly.

DESIGN

In six acromegalic patients not cured by previous treatment we compared the 24-hour GH secretion profiles under basal conditions with subcutaneous (s.c.) bolus injections of 100 micrograms octreotide every 8 hours and with continuous s.c. infusions of the same daily dose. Blood samples were taken every 10 minutes over 24 hours followed by a GHRH test (100 micrograms GHRH i.v.) with blood sampling every 15 minutes for another 2 hours. After a 4-week interval all patients were treated either by the bolus or continuous mode of octreotide application in a randomized cross-over design. On day 4 of treatment blood sampling and GHRH test were repeated. Octreotide treatment was withdrawn for another 4 weeks; all patients then received the alternate application mode and were measured under similar conditions.

MEASUREMENTS

Serum GH and plasma IGF-I concentrations were analysed by serial array averaging. IGF-I levels were measured in two different assays with and without previous protein extraction. For GH pulse detection three different algorithms (Cluster, Pulsar, Desade) were applied.

RESULTS

With both treatments, the initially elevated basal 24-hour mean serum GH concentrations (58.0 +/- 9.7 mU/l mean +/- SEM) decreased significantly (bolus: 11.5 +/- 4.9 mU/l, P < 0.001 vs basal; continuous infusion: 7.6 +/- 1.9 mU/l, P < 0.001 vs basal) after 4 days. GH suppression was significantly more pronounced following continuous infusion than bolus (P < 0.05). IGF-I plasma concentrations were lowered significantly (P < 0.05) with both forms of treatment which did not differ between themselves. Bolus and continuous infusion treatment significantly inhibited (P < 0.05) the amplitudes of pulsatile GH release, but did not change the pulse frequency. In two of the patients, GHRH stimulation did not increase GH serum levels suggesting a constitutive activation of adenylyl cyclase.

CONCLUSION

Continuous subcutaneous octreotide treatment in acromegaly suppresses mean GH levels better than bolus injection. The number of GH pulses remains unaffected by both modes of treatment providing evidence against a somatostatinergic mechanism of pulsatile GH secretion in these patients. The unchanged frequency of pulsatile GH release in the patients unresponsive to exogenous GHRH indicates that this pattern might be independent of hypothalamic GHRH and somatostatin and suggests a pituitary-derived mechanism for GH pulse generation in acromegaly.